Add script to create merged 32/64bit config.h.
Regen config.h with it (only whitespace changes).

xcode/mkconfig-h.sh

diff --git a/xcode/mkconfig-h.sh b/xcode/mkconfig-h.sh
new file mode 100755
index 0000000..43199f7
--- /dev/null
+++ b/xcode/mkconfig-h.sh
@@ -0,0 +1,12 @@
+#!/bin/sh
+
+DIR=tmp.$$
+
+mkdir -p $DIR/32 $DIR/64
+
+(cd $DIR/32; ../../../configure CFLAGS=-m32)
+(cd $DIR/64; ../../../configure CFLAGS=-m64)
+
+diff -D __LP64__ $DIR/32/config.h $DIR/64/config.h > config.h
+
+rm -r $DIR